1. Field of the Invention
The present invention relates to a laminated capacitor and more particularly to a small, high-withstanding and high-capacity laminated capacitor.
2. Description of Related Art
A laminated capacitor is shown in FIG. 3 known from the prior art. The capacitor has a structure in which external terminals 54a and 54b conduct with internal electrodes 52a and 52b, respectively in an alternating manner. The capacitor comprises a chip 53 in which a dielectric (layer) 51 and the internal electrodes 52a and 52b are laminated alternately as shown in FIG. 3. In another embodiment of the prior art capacitor, as shown in FIG. 4, a double series structure is used in which a floating internal electrode 62 which is not connected with the external terminals 54a or 54b is disposed. The floating electrode 62 is serially connected such that two dual capacitor sections 55 are formed between the internal electrodes 52a and 52b disposed so as to face each other via the dielectric 51 comprising the chip 53 and connected to the different external terminals 54a and 54b as shown in FIG. 4.
However, the conventional laminated capacitors shown in FIGS. 3 and 4 have had problems in that because a thickness of the dielectric interposed between the internal electrodes (hereinafter referred to as "element thickness") must be increased considerably to design a high-voltage withstanding capacitor, not only the value of breakdown voltage per unit thickness of the element thickness becomes low but also the electrostatic capacity which can be obtained becomes small as the element thickness increases. Accordingly, the performance of these capacitors is not adequate.
In order to solve these problems, a laminated capacitor as shown in FIG. 5 has been proposed (Unexamined Published Japanese Patent Application No. 8-037126).
This laminated capacitor has a quadruple series structure formed by alternately disposing first internal electrode groups 2 each comprising a first connected internal electrode 2a connected with one external terminal 4a, a second connected internal electrode 2b connected with another external terminal 4b and a floating internal electrode 2c positioned between the first and second connected internal electrodes 2a and 2b in the same plane and second internal electrode groups 12 each comprising a plurality (two here) of floating internal electrodes 12a disposed in a plane facing the first internal electrode group 2 via a dielectric (layer) 1 and containing no internal electrode connected to the external terminals 4a or 4b.
Because this laminated capacitor has the multiple series structure as described above and a value of breakdown voltage per element thickness (unit thickness) increases, it becomes possible to use a dielectric having thin element thickness and to increase the number of laminations because a dielectric whose element thickness is thin can be used. Accordingly, it is possible to obtain a small laminated capacitor having a large capacitance and excellent performance with respect to dielectric strength.
However, the laminated capacitor described above has had a problem in that when a distance D between edges X of the external terminals 4a and 4b and an edge a of the floating internal electrode 2c closest to the external terminals 4a and 4b among the floating internal electrodes 2c in the outermost layer is reduced below a certain degree, flashover occurs between the edges X--X of the external terminals 4a and 4b and the value of AC breakdown voltage drops.
Further, this capacitor has had a problem in that when the distance D between X-a is increased, the number of internal electrodes to be laminated must be increased to obtain a desired capacitance because an overlapped area of the internal electrodes decreases for the size of the dielectric. There has also been a problem that the AC breakdown voltage drops when the number of internal electrodes to be laminated increases.
The conventional laminated capacitor described above has had other problems because the dielectric strength performance drops when each gap G between the internal electrodes on the same plane is reduced below a certain degree and because the distance between X-a is reduced and flashover is liable to occur between the edges X--X when the gap G is increased because the floating internal electrode approaches the external terminal.